1. Field of the Invention
This invention relates to a method for correction of calibration curve in dry analytical processes which are performed for quantitative analysis of a specific component (analyte) in various fluids, typically blood.
2. Description of Prior Art
In performing an analytical process using a dry analytical element (i.e., analytical element for dry chemistry), a calibration curve showing a relationship between content or concentration of an analyte and optical denisty measured thereon is initially prepared, using a plurality of liquid samples containing the analyte in known different concentration. A concentration (this representing concentration as well as content) of the analyte in a test sampple is then determined utilizing the above-prepared calibration curve.
Generally, a calibration curve for a dry analytical element is composed of not a simple straight line but a curved line within whole measurable concentration range. Therefore, a calibration curve for the use in an precise analysis is generally prepared by graphically connecting at least three analytical data in sequence which have been determined on at least three samples having a known concentration.
It is known that characteristics of a dry analytical element slightly vary depending upon denaturation of reagents in the element in the course of storage, variation of temperature for measurement, variation of conditions for the preparation of the element, etc. This means that optical density values measured on the same liquid sample using analytical elements prepared in accordance with the same specification may fluctuate. The relationship between concentrations of the analyte and optical density values therefor can be represented by Curve B (shifted calibration curve) of FIG. 1, which is diferrent (or shifted) from Curve A (standard calibration curve). In this case, an optical density value measured on a certain liquid sample using a dry analytical element showing the shifted calibration curve is shifted from an optical density value which is ought to be given if a standard analytical element used for the preparation of the standard calibration curve is employed. In this case, if the shifted value or the variation of the calibration curve is determined in advance of or just prior to the analytical operation using the denatured (or modified, etc) analytical element, the corrected concentration of analyte is given through correcting the shifted calibration curve to accord with the standard calibration curve.
In the heretofore known method for correction of calibration curve, one or more reference liquids (i.e., liquid samples containing the analyte of a known concentration) are used for estimation of shifted optical density value, and the estimated shifted value is then subjected to calculation according to a predetermined equation for correcting the calibration curve.
In the above method, it is necessary that at least one reference liquid containing the analyte of known concentration is used. It is further necessary that at least one analytical element is used only for the procedure for the correction of calibration curve, because a dry analytical element having been used for the correction per se can be no more employed for actual analysis.
Further, the above known method for correction of calibration curve requires not only a period of time for spotting the reference liquid on a test analytical element and then photometrically determining an optical density value after incubation, but also a period of time for precisely determining the concentration of analyte in the reference liquid using another standard measuring method.
Furthermore, it is possible that the reference liquid containing the analyte of known conentration vary in its concentration of the analyte in the course of storage or due to contamination with other components. In this case, the correction of calibration curve is not precisely made.
As is described hereinbefore, a calibration curve for a dry analytical element generally is in the form of a curve, even though it contains a portion of seemingly straight line. Accordingly, it has been considered that precise correction of calibration curve requires numerical correction using a combination of a linear equation, a quadratic equation, a cubic equation, and equations of higher degree.